Let's dive into this subtraction. We'll start with 915867 and subtract 99788 from it.

Step 1: We'll start by subtracting the digit 8 and the borrow 0 from 7 in column 1 and get -1.
We add -1 to 10 and get 9 as the first digit of the result.

Step 2: We'll start by subtracting the digit 8 and the borrow 1 from 6 in column 2 and get -3.
We add -3 to 10 and get 7 as the next digit of the result.

Step 3: We'll start by subtracting the digit 7 and the borrow 1 from 8 in column 3 and get 0.
0 is the next digit of our result.

Step 4: We'll start by subtracting the digit 9 and the borrow 0 from 5 in column 4 and get -4.
We add -4 to 10 and get 6 as the next digit of the result.

Step 5: We'll start by subtracting the digit 9 and the borrow 1 from 1 in column 5 and get -9.
We add -9 to 10 and get 1 as the next digit of the result.

Step 6: We'll start by subtracting the digit 0 and the borrow 1 from 9 in column 6 and get 8.
8 is the next digit of our result.

So, 915867 - 99788 = 816079.